Fireblight: disease symptoms & treatment
Resulting in a scorched-like appearance, fireblight can have devastating consequences. Learn more about fireblight disease and how to control it.
Generally affecting plants from spring until autumn, fireblight is a bacterial disease caused by the Erwinia amylovora pathogen. It often results in the foliage looking burned or scorched. Fireblight can cause poor yields in crops and even the eventual demise of infected plants.
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Fireblight: what is it?
Introduced accidentally from North America in the 1950s, the first outbreak of fireblight disease here in the UK was recorded in 1957. Spreading via hawthorn hedges across the nation, it is now rife throughout. A notifiable disease until 2019, fireblight is now so widespread that there is no need to notify the authorities when identified on the British mainland.
Highly infectious and with the ability to spread rapidly, fireblight disease is transmitted by insects, rain and wind and contaminated plants and tools. Infections occur when the bacteria enter their host through open wounds and any blossom. Once infected, fireblight quickly spreads through the new growth into the old growth. Under warm humid conditions, it can advance by up to 5cm per day. Overwintering in cankers on infected material, fireblight then oozes out as the temperatures rise in spring ready to spread further by insect transmission.
Mainly affecting shrubs and trees of the Rosaceae family, it kills their shoots and leaves, making the plants look like they have been burnt in a fire. Along with burnt-looking foliage, fireblight symptoms include blossoms wilting and dying and branches darkening in colour as they die back. If present, fireblight can cause saplings and young specimens to die within a season and, if not controlled, mature trees within a few years.
Fireblight on pear trees, apple trees, etc.
Within the Rosaceae family, those that are most susceptible to fireblight include the pome fruits apples (Malus), pears (Pyrus), and quinces (Cydonia), and ornamentals firethorn (Pyracantha), hawthorn (Crataegus), Japanese quince (Chaenomeles), rowan (Sorbus) and serviceberry (Amelanchier). Although less of an issue, fireblight can also affect cherries, peaches and plums of the Prunus genus.
Disease signs and symptoms
Due to some similar symptoms shared with other diseases, fireblight can be hard to identify. However, here are the common symptoms of fireblight:
- Scorched or burnt-looking foliage that remains on the plant
- Wilted or dead blossoms that do not drop off
- Brown and shrivelled twigs and branches that bend to form the shape of a ‘Shepherd’s crook’
- A milky-white or brown substance oozing from branches and cankers during and after heavy rainfall or humid periods
- When the bark is peeled back, the inner wood is red-brown in colour
Fireblight can easily be confused with other bacterial and fungal diseases such as blossom wilt caused by Monilinia fungi and bacterial canker of Prunus species.
Preventing and treating fireblight
With no chemical treatments available for fireblight disease, prevention is key. Maintaining plant health and growing varieties with better resistance to fireblight can go a long way. For example, the apple varieties ‘Golden delicious’ and ‘Liberty’ and the pear variety ‘Harrow Delight’ appear to have better fireblight resistance than others.
However, due to its potential to spread rapidly, if you identify fireblight, swift action is required. With no chemical controls offered, the only cure for fireblight is removing the infected material. To control fireblight, prune out the infected wood, cutting back at least 30cm to healthy wood for thinner branches and 60cm for thicker branches. You can gently peel away the bark to see whether the inner wood is discoloured and affected. Remember to clean your pruning tools with methylated spirits between cuts to avoid spreading fireblight further. Being highly contagious, any pruned material should not be composted but disposed of carefully, ideally burned. All tools should be thoroughly disinfected with a 70% isopropyl alcohol solution.
Tip: young soft growth is particularly susceptible to fireblight disease. With this in mind, the use of nitrogen-rich fertilisers which promote vigorous new growth should be avoided in spring and summer.
Along with fireblight, apples are unfortunately susceptible to a number of other diseases. Learn more about the most common apple tree diseases here in our separate article.
